The leader of the gang instantly placing his full trust in the new guy, whom he has every reason to suspect of being a cop. Usually, this goes so far as the gang leader demoting his second-in-command to replace him with the new guy and allowing the new guy to date a female who is close family or close friend.

The Fast and the Furious is a great (?) example of that idiotic trope.

I've noticed a little pattern in some (not all) vampire movies. So we know, or learn, that the vampire is vulnerable ALL DAY as he sleeps in daylight hours, and if we can find where he is, we can waltz into his tomb around noonish and stake him. But no.. there's always a day-long trip, or some obstacle and they always get to the tomb a few minutes before sunset, and no one thinks to just hightail it out of there and come back in the morning, they always have to try to go for it and end up in a brawl or vampire breakfast. I'm more accepting of these situations when there's a manservant lurking about the tomb all day trying to ward off potential stakers, or a booby-trapped labyrinth leading to the tomb making it time-consuming to get there, but there usually isn't.